Electrochromic device with two thin glass elements and a gelled electrochromic medium

ABSTRACT

An electrochromic device comprising: a first glass element having an electrically conductive material associated therewith, wherein said first element comprises a height (h 1 ), a width (w 1 ), a thickness (t 1 ), an inner surface, and an outer surface; a second element having an electrically conductive material associated therewith, wherein said second element comprises a height (h 2 ), a width (w 2 ) , and a thickness (t 2 ), an inner surface, and an outer surface; a cell spacing (c) which comprises a distance between said inner surface of said first element and said inner surface of said second element; a gelled electrochromic medium contained within a chamber positioned between said first and second elements; wherein (h 1 ), (w 1 ), (t 1 ), (h 2 ), (w 2 ), (t 2 ), and (c) are numerical values in millimeters; and wherein (h 1 ), (w 1 ), and (t 1 ) of said first element, and (h 2 ), (w 2 ), and (t 2 ) of said second element and (c) comprise numerical values such that the following inequality is satisfied:  
             2          h   1   5          (     1   -            -   2            (       h   1     /     w   1       )     2           )             t   1   3          (     7.57   ×     10   12       )         +       2          h   2   5          (     1   -            -   2            (       h   2     /     w   2       )     2           )             t   2   3          (     7.57   ×     10   12       )           ≥     .1          (   c   )     .

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application is a continuation-in-part of U.S. applicationSer. No. 09/560,849, filed Apr. 28, 2000, which is a continuation ofU.S. application Ser. No. 09/375,136, filed Aug. 16, 1999, now U.S. Pat.No. 6,057,956, which is a continuation of U.S. application Ser. No.08/834,783, filed Apr. 2, 1997, now U.S. Pat. No. 5,940,201.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates in general to an electrochromicdevice having two thin glass elements and a free-standing gel, and moreparticularly, to a lightweight electrochromic device having afree-standing gel that cooperatively interacts with two thin glasselements to form a thick, strong unitary member which is resistant toflexing, warping, bowing, shattering and/or scattering.

[0004] 2. Background Art

[0005] Heretofore, various automatic rearview mirrors for motor vehicleshave been devised which automatically change from the full reflectance(day) mode to the partial reflectance (night) mode(s) for glareprotection purposes from light emanating from the headlights of vehiclesapproaching from the rear. The electrochromic mirrors disclosed in U.S.Pat. No. 4,902,108, entitled “Single-Compartment, Self-Erasing,Solution-Phase Electrochromic Devices Solutions for Use Therein, andUses Thereof”, issued Feb. 20, 1990, to H. J. Byker; Canadian Patent No.1,300,945, entitled “Automatic Rearview Mirror System for AutomotiveVehicles”, issued May 19, 1992, to J. H. Bechtel et al.; U.S. Pat. No.5,128,799, entitled “Variable Reflectance Motor Vehicle Mirror”, issuedJul. 7, 1992, to H. J. Byker; U.S. Pat. No. 5,202,787, entitled“Electro-Optic Device”, issued Apr. 13, 1993, to H. J. Byker et al.;U.S. Pat. No. 5,204,778, entitled “Control System For Automatic RearviewMirrors”, issued Apr. 20, 1993 to J. H. Bechtel; U.S. Pat. No.5,278,693, entitled “Tinted Solution-Phase Electrochromic Mirrors”,issued Jan. 11, 1994, to D. A. Theiste et al.; U.S. Pat. No. 5,280,380,entitled “UV-Stabilized Compositions and Methods”, issued Jan. 18, 1994,to H. J. Byker; U.S. Pat. No. 5,282,077, entitled “Variable ReflectanceMirror”, issued Jan. 25, 1994, to H. J. Byker; U.S. Pat. No. 5,294,376,entitled “Bipyridinium Salt Solutions”, issued Mar. 15, 1994, to H. J.Byker; U.S. Pat. No. 5,336,448, entitled “Electrochromic Devices withBipyridinium Salt Solutions”, issued Aug. 9, 1994, to H. J. Byker; U.S.Pat. No. 5,434,407, entitled “Automatic Rearview Mirror IncorporatingLight Pipe”, issued Jan. 18, 1995, to F. T. Bauer et al.; U.S. Pat. No.5,448,397, entitled “Outside Automatic Rearview Mirror for AutomotiveVehicles”, issued Sep. 5, 1995, to W. L. Tonar; and U.S. Pat. No.5,451,822, entitled “Electronic Control System”, issued Sep. 19, 1995,to J. H. Bechtel et al., each of which patents is assigned to theassignee of the present invention and the disclosures of each of whichare hereby incorporated herein by reference, are typical of modern dayautomatic rearview mirrors for motor vehicles. Such electrochromicmirrors may be utilized in a fully integrated inside/outside rearviewmirror system or as an inside or an outside rearview mirror system. Ingeneral, in automatic rearview mirrors of the types disclosed in theabove-referenced U.S. Patents, both the inside and the outside rearviewmirrors are comprised of a relatively thin electrochromic mediumsandwiched and sealed between two glass elements.

[0006] In most cases, when the electrochromic medium which functions asthe media of variable transmittance in the mirrors is electricallyenergized, it darkens and begins to absorb light, and the more light theelectrochromic medium absorbs the darker or lower in reflectance themirror becomes. When the electrical voltage is decreased to zero, themirror returns to its clear or substantially clear high reflectancestate. In general, the electrochromic medium sandwiched and sealedbetween the two glass elements is comprised of solution-phase,self-erasing system of electrochromic materials, although otherelectrochromic media may be utilized, including an approach wherein atungsten oxide electrochromic layer is coated on one electrode with asolution containing a redox active material to provide the counterelectrode reaction. When operated automatically, the rearview mirrors ofthe indicated character generally incorporate light-sensing electroniccircuitry which is effective to change the mirrors to the dimmedreflectance modes when glare is detected, the sandwiched electrochromicmedium being activated and the mirror being dimmed in proportion to theamount of glare that is detected. As glare subsides, the mirrorautomatically returns to its normal high reflectance state without anyaction being required on the part of the driver of the vehicle.

[0007] The electrochromic medium is disposed in a sealed chamber definedby a transparent front glass element, a peripheral edge seal, and a rearmirror element having a reflective layer, the electrochromic mediumfilling the chamber. Conductive layers are provided on the inside of thefront and rear glass elements, the conductive layer on the front glasselement being transparent while the conductive layer on the rear glasselement may be transparent or the conductive layer on the rear glasselement may be semi-transparent or opaque and may also have reflectivecharacteristics and function as the reflective layer for the mirrorassembly. The conductive layers on both the front glass element and therear glass element are connected to electronic circuitry which iseffective to electrically energize the electrochromic medium to switchthe mirror to nighttime, decreased reflectance modes when glare isdetected and thereafter allow the mirror to return to the daytime, highreflectance mode when the glare subsides as described in detail in theaforementioned U.S. Patents. For clarity of description of such astructure, the front surface of the front glass element is sometimesreferred to as the first surface, and the inside surface of the frontglass element is sometimes referred to as the second surface. The insidesurface of the rear glass element is sometimes referred to as the thirdsurface, and the back surface of the rear glass element is sometimesreferred to as the fourth surface.

[0008] Recently, electrochromic mirrors have become common on theoutside of vehicles, and suffer from the fact that they aresignificantly heavier than standard outside mirrors. This increasedweight with electrochromic mirrors exerts a strain on the mechanismsused to automatically adjust the position of the outside mirrors. Onemethod of decreasing the weight of an electrochromic mirror is byreducing the thickness of both glass elements or even remove one glassplate. For example, in solid state electrochromic devices, such as thosedescribed in U.S. Pat. No 4,973,141 to Baucke et al., where all thecomponents comprise solid state elements, e.g., solid stateelectrochromic layers (WO₃ and MoO₃), solid, hydrogen ion-conductinglayers, etc., it has been proposed that the back plate is optional. Thisis possible because the other layers are all in the solid phase andremain attached to the front plate. In electrochromic devices containingat least one solution-phase electrochromic material on the other hand,it is not possible to remove one glass plate because the solvent andelectrochromic material would leak out. Therefore, the only option forelectrochromic devices containing a solution is to decrease the glassthickness. Unfortunately, as the thickness is decreased the individualglass elements become fragile and flexible and remain that way duringand after the manufacture of an electrochromic mirror. This isespecially true as the mirrors become larger such as is needed onvehicles like sport-utility vehicles and very large trucks, e.g.,tractor-trailers. It is therefore difficult to produce a commerciallydesirable electrochromic mirror containing at least one solution-phaseelectrochromic material that has two thin glass elements because eachthin glass element will be much more likely to flex, warp, bow and/orshatter. Properties of a solution-phase electrochromic device, such ascoloring and clearing times and optical density when colored, aredependent on the thickness of the electrochromic layer (e.g., thespacing between the two glass elements). Maintaining uniform spacing isnecessary to maintain uniform appearance. The spacing between thin glasselements can be easily changed even after device manufacture by applyingsubtle pressure on one of the glass plates. This creates an undesirablenon-uniformity in the appearance of the device.

[0009] Consequently, it is desirable to provide an improvedelectrochromic device, such as an electrochromic mirror, window, etc,having a free-standing gel containing at least one solution-phaseelectrochromic material, where the gel cooperatively interacts with twothin glass elements to form a thick, strong unitary member which isresistant to flexing, warping, bowing, shattering and/or scattering andhelps maintain uniform spacing between the thin glass elements.

OBJECTS OF THE INVENTION

[0010] Accordingly, a primary object of the present invention is toprovide a lightweight electrochromic device having a free-standing gelcontaining at least one solution-phase electrochromic material, wherethe gel cooperatively interacts with two thin glass elements to form athick, strong unitary member which is resistant to flexing, warping,bowing, shattering and/or scattering.

[0011] Another object of the present invention is to provide alightweight electrochromic device having two thin glass elements thatexhibits reduced vibration, distortion and double imaging.

SUMMARY OF THE INVENTION

[0012] The above and other objects, which will become apparent from thespecification as a whole, including the drawings, are accomplished inaccordance with the present invention by providing an electrochromicdevice with thin front and rear spaced glass elements. A layer oftransparent conductive material may be placed onto the second surface,and either another layer of transparent conductive material or acombined reflector/electrode may be placed onto the third surface. Achamber is defined by the layers on the interior surfaces of the frontand rear glass elements and a peripheral sealing member. In accordancewith the present invention, the chamber contains a free-standing gelcomprising a solvent and a crosslinked polymer matrix, and furthercontains at least one electrochromic material in solution with thesolvent and interspersed in the crosslinked polymer matrix, where thegel cooperatively interacts with the thin glass elements to form athick, strong unitary member which is resistant to flexing, warping,bowing, shattering and/or scattering, and further allows the mirror toexhibit reduced vibration, distortion and double imaging.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The subject matter which is regarded as the invention isparticularly pointed out and distinctly claimed in the concludingportion of the specification. The invention, together with furtherobjects and advantages thereof, may best be understood by reference tothe following description taken in connection with the accompanyingdrawings, where like numerals represent like components, in which:

[0014]FIG. 1 is a front elevational view schematically illustrating aninside/outside electrochromic device for motor vehicles where the insideand outside mirrors incorporate the mirror assembly of the presentinvention; and

[0015]FIG. 2 is an enlarged cross-sectional view of the insideelectrochromic device incorporating a free-standing gel cooperativelyinteracting with two thin glass elements illustrated in FIG. 1, taken onthe line 2-2′ thereof.

DETAILED DESCRIPTION OF THE INVENTION

[0016]FIG. 1 shows a front elevational view schematically illustratingan inside mirror assembly 110 and two outside rearview mirror assemblies111 a and 111 b for the driver-side and passenger-side, respectively,all of which are adapted to be installed on a motor vehicle in aconventional manner and where the mirrors face the rear of the vehicleand can be viewed by the driver of the vehicle to provide a rearwardview. Inside mirror assembly 110, and outside rearview mirror assemblies111 a and 111 b may incorporate light-sensing electronic circuitry ofthe type illustrated and described in the above-referenced CanadianPatent No. 1,300,945; U.S. Pat. No. 5,204,778; or U.S. Pat. No.5,451,822, and other circuits capable of sensing glare and ambient lightand supplying a drive voltage to the electrochromic element. Mirrorassemblies 110, 111 a and 111 b are essentially identical in that likenumbers identify components of the inside and outside mirrors. Thesecomponents may be slightly different in configuration but function insubstantially the same manner and obtain substantially the same resultsas similarly numbered components. For example, the shape of the frontglass element of inside mirror 110 is generally longer and narrower thanoutside mirrors 111 a and 111 b. There are also some differentperformance standards placed on inside mirror 110 compared with outsidemirrors 111 a and 111 b. For example, inside mirror 110 generally, whenfully cleared, should have a reflectance value of about 70 percent toabout 80 percent or higher whereas the outside mirrors often have areflectance of about 50 percent to about 65 percent. Also, in the UnitedStates (as supplied by the automobile manufacturers), the passenger-sidemirror 111 b typically has a spherically bent, or convex shape, whereasthe driver-side mirror 111 a, and inside mirror 110 presently must beflat. In Europe the driver-side mirror 111 a is commonly flat oraspheric, whereas the passenger-side mirror 111 b has a convex shape. InJapan both mirrors have a convex shape. The following description isgenerally applicable to all mirror assemblies of the present invention.

[0017] Rearview mirrors embodying the present invention preferablyinclude a bezel 144, which extends around the entire periphery of eachindividual assembly 110, 111 a and/or 111 b. The bezel 144 conceals andprotects the spring clips (not shown) and the peripheral edge portionsof sealing member and both the front and rear glass elements (describedbelow). A wide variety of bezel designs are well known in the art, suchas, for example the bezel taught and claimed in above-referenced U.S.Pat. No. 5,448,397. There are also a wide variety of housing well knownin the art for attaching the mirror assembly 110 to the inside frontwindshield of an automobile, or for attaching the mirror assemblies 111a and 111 b to the outside of an automobile. A preferred housing forattaching an inside assembly is disclosed in above-referenced U.S. Pat.No. 5,337,948.

[0018] The electrical circuit preferably incorporates an ambient lightsensor (not shown) and a glare light sensor 160, the glare light sensorbeing positioned either behind the mirror glass and looking through asection of the mirror with the reflective material completely orpartially removed, or the glare light sensor can be positioned outsidethe reflective surfaces, e.g., in the bezel 144. Additionally, an areaor areas of the electrode and reflector, such as 146 or the area alignedwith sensor 160, may be completely removed, or partially removed in, forexample, a dot or line pattern, to permit a vacuum fluorescent display,such as a compass, clock, or other indicia, to show through to thedriver of the vehicle. Co-filed U.S. patent application entitled “ANINFORMATION DISPLAY AREA ON ELECTROCHROMIC MIRRORS HAVING A THIRDSURFACE REFLECTOR” shows a presently preferred line pattern. The presentinvention is also applicable to a mirror which uses only one video chiplight sensor to measure both glare and ambient light and which isfurther capable of determining the direction of glare. An automaticmirror on the inside of a vehicle, constructed according to thisinvention, can also control one or both outside mirrors as slaves in anautomatic mirror system.

[0019]FIG. 2 shows a cross-sectional view of mirror assembly 110 alongthe line 2-2′. Mirror 110 has a front transparent element 112 having afront surface 112 a and a rear surface 112 b, and a rear element 114having a front surface 114 a and a rear surface 114 b. Since some of thelayers of the mirror are very thin, the scale has been distorted forpictorial clarity. Also, for clarity of description of such a structure,the following designations will be used hereinafter. The front surfaceof the front glass element will be referred to as the first surface andthe back surface of the front glass element as the second surface. Thefront surface of the rear glass element will be referred to as the thirdsurface, and the back surface of the rear glass element as the fourthsurface. Chamber 116 is defined by one or more layers of transparentconductive material 118 (disposed on front element rear surface 112 b),another layer disposed on rear element front surface 114 a comprisingeither a transparent conductive material 120 or a combinationreflector/electrode, and an inner circumferential wall 121 of sealingmember 122. Typically electrochromic mirrors are made with glasselements having a thickness of about 2.3 mm. The preferred thin glasselements according to the present invention have thicknesses of about1.0 mm, which results in a weight savings of more than 50%. Thisdecreased weight ensures that the mechanisms used to manipulate theorientation of the mirror, commonly referred to as carrier plates, arenot overloaded and further provides significant improvement in thevibrational stability of the mirror. As will be discussed in greaterdetail below, the preferred thickness of the elements can vary greatlydepending upon, among other things, the associated geometricconfiguration (i.e. the width and height) of the elements.

[0020] Front transparent element 112 may be any material which is thinand transparent and has sufficient strength to be able to operate in theconditions, e.g., varying temperatures and pressures, commonly found inthe automotive environment. Front element 112 may comprise any type ofglass, borosilicate glass, soda lime glass, float glass or any othermaterial, such as, for example, a polymer or plastic, that istransparent in the visible region of the electromagnetic spectrum. Forpurposes of the present example, front element 112 is preferably a sheetof glass with a thickness ranging from approximately 0.5 mm toapproximately 1.5 mm. More preferably front element 112 has a thicknessranging from approximately 0.8 mm to approximately 1.2 mm, with thepresently most preferred thickness about 1.0 mm—for a small areaelectrochromic mirror. Rear element 114 must meet the operationalconditions outlined above, except that it does not need to betransparent, and therefore may comprise polymers, metals, glass,ceramics, and preferably is a sheet of glass with a thickness in thesame ranges as element 112.

[0021] When both glass elements are made thin the vibrational propertiesof an interior or exterior mirror improve—although the effects are moresignificant for exterior mirrors. These vibrations, that result from theengine running and/or the vehicle moving, affect the rearview mirror,such that the mirror essentially acts as a weight on the end of avibrating cantilever beam. This vibrating mirror causes blurring of thereflected image that is a safety concern as well as a phenomenon that isdispleasing to the driver. As the weight on the end of the cantileverbeam (i.e., the mirror element attached to the carrier plate on theoutside mirror or the mirror mount on the inside mirror) is decreasedthe frequency at which the mirror vibrates increases. If the frequencyof the mirror vibration increases to around 60 Hertz the blurring of thereflected image is not visually displeasing to the vehicle occupants.Moreover, as the frequency at which the mirror vibrates increases thedistance the mirror travels while vibrating decreases significantly.Thus, by decreasing the weight of the mirror element the complete mirrorbecomes more vibrationally stable and improves the ability of the driverto view what is behind the vehicle. For example, an interior mirror withtwo glass elements having a thickness of 1.1 mm has a first modehorizontal frequency of about 55 Hertz whereas a mirror with two glasselements of 2.3 mm has a first mode horizontal frequency of about 45Hertz. This 10 Hertz differences produces a significant improvement inhow a driver views a reflected image.

[0022] No electrochromic mirrors and/or devices incorporating two thinglass elements and containing a solution-phase electrochromic materialhave been commercially available because thin glass suffers from beingflexible and therefore is prone to warping, flexing and bowing,especially when exposed to extreme environments. Thus, in accordancewith the present invention, chamber 116 contains a free-standing gelthat cooperatively interacts with thin glass elements 112 and 114 toproduce a mirror that acts as one thick unitary member rather than twothin glass elements held together only by a seal member. Infree-standing gels, which contain a solution and a cross-linked polymermatrix, the solution is interspersed in a polymer matrix and continuesto function as a solution. Also, at least one solution-phaseelectrochromic material is in solution in the solvent and therefore aspart of the solution is interspersed in the polymer matrix (thisgenerally being referred to as “gelled electrochromic medium” 124). Thisallows one to construct a rearview mirror or other electrochromic devicewith thinner glass in order to decrease the overall weight of the mirrorwhile maintaining sufficient structural integrity so that the mirrorwill survive the extreme conditions common to the automobileenvironment. This also helps maintain uniform spacing between the thinglass elements which improves uniformity in the appearance (e.g.,coloration) of the mirror. This structural integrity results because thefree-standing gel, the first glass element 112, and the second glasselement 114, which individually have insufficient strengthcharacteristics to work effectively in an electrochromic mirror, couplein such a manner that they no longer move independently but act as onethick unitary member. This stability includes, but is not limited to,resistance to, flexing, warping, bowing and breaking, as well asimproved image quality of the reflected image, e.g., less distortion,double image, color uniformity and independent vibration of each glasselement. However, while it is important to couple the front and rearglass elements, it is equally important (if not more so) to ensure thatthe electrochromic mirror functions properly. The free-standing gel mustbond reasonably well to the electrode layers (including thereflector/electrode if the mirror has a third surface reflector) on thewalls of such a device, but not substantially interfere with theelectron transfer between the electrode layers and the electrochromicmaterial(s) disposed in the chamber 116. Further, the gel must notmaterially shrink, craze or weep over time such that the gel itselfcauses poor image quality. Ensuring that the free-standing gel bondswell enough to the electrode layers to couple the front and rear glasselements and does not deteriorate over time, while allowing theelectrochromic reactions to take place as though they were in solutionis an important aspect of the present invention.

[0023] It will be understood that in addition to a solution-phaseelectrochromic medium, a hybrid electrochromic medium is likewisecontemplated for use. In a hybrid electrochromic medium, one of thecathodic or anodic materials can be applied (in a solid form) to itsrespective electrically conductive or semi-conductive material. Forexample, tungsten oxide (WO₃) or polyaniline can be applied onto thesurface of a conventional electrically conductive material.Additionally, numerous viologens can be applied onto, among othermaterials, TiO₂.

[0024] To perform adequately a mirror must accurately represent thereflected image, and this cannot be accomplished when the glass elements(to which the reflector is attached) tend to bend or bow while thedriver is viewing the reflected image. The bending or bowing occursmainly due to pressure points exerted by the mirror mounting andadjusting mechanisms and by differences in the coefficients of thermalexpansion of the various components that are used to house the exteriormirror element. These components include a carrier plate used to attachthe mirror element to the mechanism used to manipulate or adjust theposition of the mirror (bonded to the mirror by an adhesive), a bezeland a housing. Many mirrors also typically have a potting material as asecondary seal. Each of these components, materials and adhesives havevarying coefficients of thermal expansion that will expand and shrink tovarying degrees during heating and cooling and will exert stress on theglass elements 112 and 114. On very large applications, includingmirrors and windows hydrostatic pressure becomes a concern and may leadto double imaging problems when the front and rear glass elements bowout at the bottom and bow in at the top of the mirror or window. Bycoupling the front and rear glass elements the thin glass/free-standinggel/thin glass combination act as one thick unitary member (while stillallowing proper operation of the electrochromic mirror or window) andthereby reduce or eliminate the bending, bowing, flexing, double imageand distortion problems and non-uniform coloring of the electrochromicmedium.

[0025] The cooperative interaction between the free-standing gel and thethin glass elements of the present invention also improves the safetyaspects of the electrochromic mirror 110 having thin glass elements. Inaddition to being more flexible, thin glass is more prone to breakagethan thick glass. By coupling the free-standing gel with the thin glassthe overall strength is improved (as discussed above) and furtherrestricts shattering and scattering and eases clean-up in the case ofbreakage of the device.

[0026] The improved cross-linked polymer matrix used in the presentinvention is disclosed in commonly assigned co-pending U.S. patentapplication Ser. No. 08/616,967 entitled “IMPROVED ELECTROCHROMIC LAYERAND DEVICES COMPRISING SAME” filed on Mar. 15, 1996, and theInternational Patent Application filed on or about Mar. 15, 1997 andclaiming priority to this U.S. Patent Application. The entire disclosureof these two Applications, including the references contained therein,are hereby incorporated herein by reference.

[0027] Generally, the polymer matrix results from crosslinking polymerchains, where the polymer chains are formed by the vinyl polymerizationof a monomer having the general formula:

[0028] where R₁ is optional and may be selected from the groupconsisting of: alkyl, cycloalkyl, poly-cycloalkyl, heterocycloalkyl,carboxyl and alkyl and alkenyl derivatives thereof; alkenyl,cycloalkenyl, cycloalkadienyl, poly-cycloalkadienyl, aryl and alkyl andalkenyl derivatives thereof, hydroxyalkyl; hydroxyalkenyl; alkoxyalkyl;and alkoxyalkenyl where each of the compounds has from approximately 1to approximately 20 carbon atoms. R₂ is optional and may be selectedfrom the group consisting of alkyl, cycloalkyl, alkoxyalkyl, carboxyl,phenyl and keto where each of the compounds has from approximately 1 toapproximately 8 carbon atoms; and oxygen. R₃, R₄, and R₅ may be the sameor different and may be selected from the group consisting of: hydrogen,alkyl, cycloalkyl, poly-cycloalkyl, heterocycloalkyl, and alkyl andalkenyl derivatives thereof; alkenyl, cycloalkenyl, cycloalkadienyl,poly-cycloalkadienyl, aryl and alkyl and alkenyl derivatives thereof;hydroxyalkyl; hydroxyalkenyl; alkoxyalkyl; alkoxyalkenyl; keto;acetoacetyl; vinyl ether and combinations thereof, where each of thecompounds has from approximately 1 to approximately 8 carbon atoms.Finally, B may be selected from the group consisting of hydroxyl;cyanato; isocyanato; isothiocyanato; epoxide; silanes; ketenes;acetoacetyl, keto, carboxylate, imino, amine, aldehyde and vinyl ether.However, as will be understood by those skilled in the art, if B is ancyanato, isocyanato, isothiocyanato, or aldehyde it is generallypreferred that R₁, R₂, R₃, R₄, and R₅ not have a hydroxyl functionality.Preferred among the monomers is methyl methacrylate; methyl acrylate;isocyanatoethyl methacrylate; 2-isocyanatoethyl acrylate; 2-hydroxyethylmethacrylate; 2-hydroxyethyl acrylate; 3-hydroxypropyl methacrylate;glycidyl methacrylate; 4-vinylphenol; acetoacetoxy methacrylate andacetoacetoxy acrylate.

[0029] Electrochromic devices are sensitive to impurities, which isshown through poor cycle life, residual color of the electrochromicmaterial in its bleached state, and poor UV stability. Although manycommercial precursors are fairly pure and perform adequately as ordered,purification would improve their performance. They can not, however, bereadily purified by distillation because their low vapor pressure makeseven vacuum distillation difficult or impossible. On the other hand, themonomers used to make the polymer matrix can be purified and thus are asignificant advance in ensuring proper performance of an electrochromicdevice. This purification may be through chromatography, distillation,recrystalization or other purification techniques well known in the art.

[0030] The monomers of the preferred embodiment of the present inventionshould also preferably be capable of pre-polymerization, typically inthe solvent utilized in the final electrochromic mirror. Bypre-polymerization we mean that the monomers and/or precursors reactwith one another to produce relatively long and relatively linearpolymers. These polymer chains will remain dissolved in the solvent andcan have molecular weights ranging from about 1,000 to about 300,000,although those skilled in the art will understand that molecular weightsof up to 3,000,000 are possible under certain conditions.

[0031] It should be understood that more than one monomer may bepre-polymerized together. Equation [I] shows the general formula for themonomers of the preferred embodiment of the present invention.Generally, any of the combinations of the monomers shown may be combinedinto one or more polymers (i.e., a polymer, a copolymer, terpolymer,etc.) in the pre-polymerization process. For example, one monomer may bepolymerized to give a homogeneous polymer material such as poly(2-hydroxyethyl methacrylate), poly (2-isocyanatoethyl methacrylate),and the like. However, it is generally preferred that a species with acrosslinking reactive component (e.g., hydroxyl, acetoacetyl,isocyanate, thiol etc.) be combined with another species either havingthe same crosslinking reactive component or no crosslinking reactivecomponent (e.g., methyl methacrylate, methyl acrylate, etc.). If acopolymer is produced, the ratio of the monomers without and with thecrosslinking components may range from about 200:1 to about 1:200. Anexample of these copolymers include hydroxyethyl methacrylate (HEMA)combined with methyl methacrylate (MMA) to form a copolymer. The ratioof HEMA to MMA may range form about 1:3 to about 1:50 with the preferredratio being about 1:10. The preferred crosslinker for any of thepre-polymers having a hydroxyl (or any reactive group having an activehydrogen, such as thiol, hydroxyl, acetoacetyl, urea, melamine,urethane, etc.) is an isocyanate, isothiocyanate, and the like having afunctionality greater than one. Also, 2-isocyanatoethyl methacrylate(IEMA) may be combined with MMA in the ratio of about 1:3 to about 1:50with the preferred ratio of about 1:10. Crosslinking of any of thepolymer chains containing an isocyanate can occur with any di- orpoly-functional compound containing a reactive hydrogen, such ashydroxyl, thiol, acetoacetyl, urea, melamine, urethanes, with hydroxylbeing presently preferred. These must have a functionality greater thanone and may be the same as those described hereinabove, aliphatic oraromatic compounds or, preferably, may be 4,4′-isopropylidenediphenol,4-4′(1-4 phenylenediisopropylidene) bisphenol, 4-4′(1-3phenylenediisopropylidene), or bisphenol 1,3-dihydroxy benzene. Althoughthe above description relates to copolymers, it will be understood bythose skilled in the art that more complex structures (terpolymers,etc.) may be made using the same teachings.

[0032] Finally, two copolymers may be combined such that they crosslinkwith one another. For example HEMA/MMA may be combined with IEMA/MMA andthe hydroxyl groups of HEMA will self-react with the isocyanate groupsof IEMA to form an open polymeric structure. It should be understoodthat the rates of crosslinking for any of the polymers described hereincan be controlled by proper selection of the reactive crosslinkingspecies employed. For example, reaction rates can be increased by usingan aromatic isocyanate or an aromatic alcohol or both. Reaction ratescan be decreased, for example, by using sterically hindered isocyanatesor sterically hindered alcohols or both.

[0033] It should also be noted that the rigidity of the free standinggel can be altered by changing the polymer molecular weight, the weightpercent of the polymer and the crosslink density of the polymer matrix.The gel rigidity generally increases with increasing polymerconcentration (weight percent), increasing crosslink density and to someextent with increasing molecular weight.

[0034] During operation, light rays enter through the front glass 112,the transparent conductive layer(s) 118, the free-standing gel and atleast one electrochromic material in chamber 116, the transparentconductive layer 120 and the back glass 114, before being reflected fromthe reflector 124 provided on the fourth surface 114 b of the mirror110. Light in the reflected rays exit by the same general path traversedin the reverse direction. Both the entering rays and the reflected raysare attenuated in proportion to the degree to which the gelledelectrochromic medium 124 is light absorbing. Alternatively, as statedabove, the reflector may be placed on the third surface 114 a inaccordance with the disclosure of U.S. patent application entitled“ELECTROCHROMIC REARVIEW MIRROR INCORPORATING A THIRD SURFACE METALREFLECTOR” filed on or about Apr. 2, 1997. The entire disclosure of thisU.S. patent application is hereby incorporated herein by reference. Inthis case the third surface reflector doubles as an electrode and thetransparent conductive layer 120 may optionally be deleted. Further, ifthe reflector is placed on the third surface 114 a, a heater 138 may beplaced on the fourth surface 114 b in accordance with the teachings inthe immediately above-referenced U.S. patent application.

[0035] The at least one electrochromic material may be a wide variety ofmaterials capable of changing properties such that light travelingtherethrough is attenuated but must be capable of being dissolved in thesolvent. In order to balance charge during the electrochromic reactions,another redox active material must be present. This other material mayinclude solution-phase redox, solid-state, and metal or viologen saltdeposition; however, solution phase redox is presently preferred, suchas those disclosed in above-referenced U.S. Pat. Nos. 4,902,108;5,128,799, 5,278,693; 5,280,380; 5,282,077; 5,294,376; 5,336,448.

[0036] One or more layers of a transparent electrically conductivematerial 118 are deposited on the second surface 112 b to act as anelectrode. Transparent conductive material 118 may be any materialwhich: bonds well to front element 112 and maintains this bond when theepoxy seal 122 bonds thereto; is resistant to corrosion with anymaterials within the electrochromic device; is resistant to corrosion bythe atmosphere; and has minimal diffuse or specular reflectance, highlight transmission, neutral coloration and good electrical conductance.Transparent conductive material 118 may be fluorine doped tin oxide,indium doped tin oxide (ITO), ITO/metal/ITO (IMI) as disclosed in“Transparent Conductive Multilayer-Systems for FPD Applications”, by J.Stollenwerk, B. Ocker, K. H. Kretschmer of LEYBOLD AG, Alzenau, Germany,and the materials described in above-referenced U.S. Pat. No. 5,202,787,such as TEC 20 or TEC 15, available from Libbey Owens-Ford Co. (LOF) ofToledo, Ohio. Similar requirements are needed for whatever is depositedonto the third surface 114 a, whether it is another layer of transparentconductive material 120 (in the case of a window) or a combinedreflector/electrode (in the case of a mirror).

[0037] The conductance of transparent conductive material 118 willdepend on its thickness and composition, but as a general ruleatmospheric pressure chemical vapor deposition (APCVD) applied coatings,such as TEC coatings from LOF, are cheaper than vacuum-depositedcoatings, such as ITO coatings, and more importantly they are morecolor-neutral. This color neutrality of the coatings is especiallypronounced when the mirrors are in their full colored or darkened statebecause in this dark state the primary sources of the reflection viewedby a vehicle occupant are the reflections from the first and secondsurface of the device. Thus, the transparent coating 118 disposed on thesecond surface 112 b has a greater influence on the color neutrality ofthe device when the device is in a highly or full darkened state.Another factor to be considered is that, although both ITO and the TECcoatings will work as transparent conductors in mirrors having thickglass elements, the TEC coatings cannot to date be applied onto glasshaving a thickness less than about 2 mm while the glass is on theproduction float-line used to manufacture sheets of glass. Thus, TECcoatings are not presently available on thin glass. This leads to colormatching problems because there are cases where it is beneficial to havean interior mirror with low cost thick glass elements and an exteriormirror with light weight thin glass elements and have both mirrors onthe same vehicle. The inside mirror (110 in FIG. 1) having thick glasscan use the inexpensive TEC coatings on the second surface andtherefore, when the mirror is in the darkened state, the reflected imageis color-neutral. However, the outside mirrors (111 a and/or 111 b ofFIG. 1) having thin glass must use the expensive ITO coatings on thesecond surface and therefore, when the mirror is in the darkened state,the reflected image is not completely color-neutral— and therefore notcolor-matched with the inside mirror.

[0038] In addition, TEC coatings can cause difficulties when applied toglass that must then be bent or curved to a convex or aspheric shape,irrespective of the thickness of the glass, because each glass elementmust have a substantially similar radius of curvature. The TEC coatingsare applied during the manufacture of the glass to the side of the glassthat is not in contact with the tin bath or the rollers (i.e., thedeposition is on the “clean” side of the glass). Since the glass bendingprocess occurs after the glass is produced, the TEC coatings are presenton the glass surface when the glass is bent. During the bending processthe glass element is heated to high temperatures, and although notknowing the exact mechanism, it is believed that the difference in thecoefficient of thermal expansion between the glass and the conductivecoating, and/or the difference in emissivity between the coated anduncoated sides of the glass, tend to alter the flexing properties of thecombined glass/coating structure during cooling. If a mirror with afourth surface reflector is produced, then the TEC coatings will beplaced on the second (concave) and third (convex) surfaces, and becauseof the altered flexing properties, each glass element will have adifferent radius of curvature. If a mirror with a third surfacereflector is produced, two problems occur. First, to get similar radiiof curvature, a TEC coating must be placed on the second and fourthsurfaces, but the fourth surface TEC coating is essentially useless anddoes nothing but increase the unit price of the mirror. Second, thereflector/electrode that is applied to the third surface has to beapplied to the “dirty” side of the glass that was in contact with thetin bath and the rollers. This leads to problems well known in the artsuch as tin bloom, sulfur stain and roller marks, all of which causeadverse side effects in electrochromic mirrors. ITO coatings can beapplied to the second surface after the glass is bent to alleviate theseproblems, however, this leads to the same color-neutrality andcolor-matching problems outlined above.

[0039] In accordance with another aspect of the present invention, amultilayer color-neutral transparent conductive coating 118 can be usedon the second surface of an exterior mirror (111 a and/or 111 b ofFIG. 1) having thin or bent glass, in combination with an interiormirror having TEC coatings on the second surface such that themirror-system is color-neutral and color-matched. This color-neutraltransparent conductive coating includes a thin (e.g., between about 150angstroms and about 500 angstroms) first transparent layer 118 a havinga high refractive index, followed by thin (e.g., between about 150angstroms and about 500 angstroms) second transparent layer 118 b havinga low refractive index, followed by a thick (e.g., between about 800angstroms and about 3500 angstroms) third conductive transparent layer118 c having a high refractive index. Glass has a refractive index ofabout 1.5; the first two thin layers generally having refractive indicesof about 2.0 and about 1.5, respectively, tend to act in concert to formone layer having a medium refractive index of about 1.75. The thick topcoating has a refractive index of about 2.0. Thus a stack is producedhaving refractive indices of approximately 1.5/1.75/2.0. The presentlypreferred compositions and thicknesses for each layer of the multi-layerstack are: about 200-400 angstroms of ITO for the first layer 118 a;about 200-400 angstroms of SiO₂ for the second layer 118 b and about1500 angstroms of ITO for the third layer 118 c. This gradation betweenlow and high refractive indices produces a transparent conductivecoating that is color-neutral, which matches the color-neutral TECcoatings on the second surface of the inside mirror—leaving aninside/outside color-matched mirror system.

[0040] In accordance with yet another embodiment of the presentinvention, an additional advantage of thin glass construction isimproved optical image quality for convex, aspheric and allelectrochromic devices, including mirrors and windows that are not flat.It is difficult to reproducibly bend glass and obtain identical localand global radii of curvature for each pair of glass elements. However,most electrochromic mirrors are made by bonding two glass elementstogether in a nominally parallel, planar, spaced-apart relationship andany deviation from parallelism manifests itself as distortion, doubleimage and non-uniform spacing between the two glass elements. The doubleimage phenomena is due to mismatch in the curvature of the glasselements which results in misalignment between the residual andsecondary reflections from the front glass element and its transparentconducting coating and the reflections from the main reflector layer.This is extensively discussed in above-referenced U.S. patentapplication entitled “ELECTROCHROMIC REARVIEW MIRROR INCORPORATING ATHIRD SURFACE METAL REFLECTOR”. Changing the reflector layer from thefourth surface to the third surface helps reduce double imaging becausethe distance between the first surface, residual reflectance, and thereflectance form the main reflector is reduced. This is especiallybeneficial for mirrors using bent glass. Combining the use of a thirdsurface reflector layer with the use of a thin glass front elementprovides a remarkable advantage for mirrors using bent glass since theresidual and the main reflections are so close there is little or nodouble image. This is the case even when the glass is bent in normalbending processes that give rise to significant variations in the localand overall radius of curvature between the two glass elements used tomake the mirror. The combination of a third surface reflector/electrodeand thin glass front element provides a mirror that nearly equals theoptical image quality of a true first surface reflector mirror even whenthe glass is bent.

[0041] The coating 120 of the third surface 114 a is sealably bonded tothe coating 118 on the second surface 112 b near their outer perimetersby a sealing member 122. Preferably, sealing member 122 contains glassbeads (not shown) to hold transparent elements 112 and 114 in a paralleland spaced apart relationship while the seal material cures. Sealingmember 122 may be any material which is capable of adhesively bondingthe coatings on the second surface 112 b to the coatings on the thirdsurface 114 a to seal the perimeter such that electrochromic material124 does not leak from chamber 116 while simultaneously maintaining agenerally constant distance therebetween. Optionally, the layer oftransparent conductive coating 118 and the layer on the third surface120 (transparent conductive material or reflector/electrode) may beremoved over a portion where sealing member is disposed (not the entireportion, otherwise the drive potential could not be applied to the twocoatings). In such a case, sealing member 118 must bond well to glass.

[0042] The performance requirements for a perimeter seal member 122 usedin an electrochromic device are similar to those for a perimeter sealused in a liquid crystal device (LCD) which are well known in the art.The seal must have good adhesion to glass, metals and metal oxides, musthave low permeabilities for oxygen, moisture vapor and other detrimentalvapors and gases, and must not interact with or poison theelectrochromic or liquid crystal material it is meant to contain andprotect. The perimeter seal can be applied by means commonly used in theLCD industry such as by silk-screening or dispensing. Totally hermeticseals such as those made with glass frit or solder glass can be used,but the high temperatures involved in processing (usually near450-degrees Centigrade) this type of seal can cause numerous problemssuch as glass substrate warpage, changes in the properties oftransparent conductive electrode and oxidation or degradation of thereflector. Because of their lower processing temperatures,thermoplastic, thermosetting or UV curing organic sealing resins arepreferred. Such organic resin sealing systems for LCD's are described inU.S. Pat. Nos. 4,297,401, 4,418,102, 4,695,490, 5,596,023 and 5,596,024.Because of their excellent adhesion to glass, low oxygen permeabilityand good solvent resistance, epoxy based organic sealing resins arepreferred. These epoxy resin seals may be UV curing, such as describedin U.S. Pat. No. 4,297,401, or thermally curing, such as with mixturesof liquid epoxy resin with liquid polyamide resin or dicyandiamide, orthey can be homopolymerized. The epoxy resin may contain fillers orthickeners to reduce flow and shrinkage such as fumed silica, silica,mica, clay, calcium carbonate, alumina, etc., and/or pigments to addcolor. Fillers pretreated with hydrophobic or silane surface treatmentsare preferred. Cured resin crosslink density can be controlled by use ofmixtures of mono-functional, di-functional and multi-functional epoxyresins and curing agents. Additives such as silanes or titanates can beused to improve the seal's hydrolytic stability, and spacers such asglass beads or rods can be used to control final seal thickness andsubstrate spacing. Suitable epoxy resins for use in a perimeter sealmember 122 include but are not limited to: “EPON RESIN” 813, 825, 826,828, 830, 834, 862, 1001F, 1002F, 2012, DPS-155, 164, 1031, 1074, 58005,58006, 58034, 58901, 871, 872 and DPL-862 available from Shell ChemicalCo., Houston, Tex.; “ARALITE” GY 6010, GY 6020, CY 9579, GT 7071, XU248, EPN 1139, EPN 1138, PY 307, ECN 1235, ECN 1273, ECN 1280, MT 0163,MY 720, MY 0500, MY 0510 and PT 810 available from Ciba Geigy,Hawthorne, N.Y.; “D.E.R.” 331, 317, 361, 383, 661, 662, 667, 732, 736,“D.E.N.” 431, 438, 439 and 444 available from Dow Chemical Co., Midland,Mich. Suitable epoxy curing agents include V-15, V-25 and V-40polyamides from Shell Chemical Co.; “AJICURE” PN-23, PN-34 and VDHavailable from Ajinomoto Co., Tokyo, Japan; “CUREZOL” AMZ, 2MZ, 2E4MZ,C11Z, C17Z, 2PZ, 21Z and 2P4MZ available from Shikoku Fine Chemicals,Tokyo, Japan; “ERISYS” DDA or DDA accelerated with U-405, 24EMI, U-410and U-415 available from CVC Specialty Chemicals, Maple Shade, N.J..;“AMICURE” PACM, 352, CG, CG-325 and CG-1200 available from Air Products,Allentown, Pa. Suitable fillers include fumed silica such as “CAB-O-SIL”L-90, LM-130, LM-5, PTG, M-5, MS-7, MS-55, TS-720, HS-5, EH-5 availablefrom Cabot Corporation, Tuscola, Ill.; “AEROSIL” R972, R974, R805, R812,R812 S, R202, US204 and US206 available from Degussa, Akron, Ohio.Suitable clay fillers include BUCA, CATALPO, ASP NC, SATINTONE 5,SATINTONE SP-33, TRANSLINK 37, TRANSLINK 77, TRANSLINK 445, TRANSLINK555 available from Engelhard Corporation, Edison, N.J. Suitable silicafillers are SILCRON G-130, G-300, G-100-T and G-100 available from SCMChemicals, Baltimore, Md. Suitable silane coupling agents to improve theseal's hydrolytic stability are Z-6020, Z-6030, Z-6032, Z-6040, Z-6075and Z-6076 available from Dow Corning Corporation, Midland, Mich.Suitable precision glass microbead spacers are available in anassortment of sizes from Duke Scientific, Palo Alto, Calif.

[0043] In the assembly and manufacture of electrochromic devicespolymeric beads may be applied to the electrochromic mirror area on theviewing area of the second or third surface, i.e., inboard of theperimeter seal, to temporarily maintain proper cell spacing during themanufacturing process. These beads are even more useful with deviceshaving thin glass elements because they help prevent distortion anddouble image during device manufacture and maintain a uniformelectrochromic medium thickness until gellation occurs. It is desirablethat these beads comprise a material that will dissolve in theelectrochromic medium and is benign to the electrochromic system whilebeing compatible with whatever electrochromic system is contained withinthe chamber 116 (e.g., the constituents of gelled layer 124). While theuse of PMMA beads is known, they are not preferred because they have thefollowing disadvantages: they require a heat cycle (generally at least 2hours at 85 degrees C.) to dissolve, they do not dissolve before thepreferred gels of the present invention crosslink, they can cause lightrefracting imperfections in gelled and non-gelled electrochromicdevices, and they can cause the electrochromic medium to color and clearmore slowly near the area where beads were prior to dissolving.

[0044] In accordance with another aspect of the present invention,polymeric beads 117, that dissolve within an electrochromic device atambient or near-ambient temperatures without imparting refractiveimperfections, are placed or sprinkled on the second or third surfacewithin the viewing area of the mirror or a window so that they preventdistortion and maintain cell spacing during manufacturing and dissolvevery soon thereafter.

[0045] The polymeric beads 117 can be incorporated into anelectrochromic mirror as follows: The perimeter sealing resin is chargedwith glass beads of the appropriate size desired for the final cell gap(typically around 135 microns in diameter for a solution-phase insideelectrochromic mirror) at a level of about ½ weight percent. Drypolymeric beads 117 that are sized about 10% larger than the glass beadsare loaded into a “salt shaker” type container with holes on one end.The rear glass element 114 is laid flat with the inside electrodesurface (third surface) facing up. Plastic beads are sprinkled onto thecoating (120) disposed on the third surface 114 a using the salt shakerto a concentration of about 5 to 10 beads per square centimeter. Theperimeter sealing member 122 is applied around the edges of the surfaceof the transparent conductive electrode on the rear surface of the frontelement 112 by dispensing or silk screening as is typical for themanufacture of LCD's, such that seal material covers the entireperimeter except for a gap of about 2 mm along one edge. This gap in theseal will be used as a fill port (not shown) to introduce theelectrochromic medium after assembly of the glass plates and curing ofthe seal. After seal application, the glass plates are assembledtogether by laying the first glass plate on top of the second glassplate and the assembly is pressed until the gap between the glass platesis determined by the glass and plastic spacers. The sealing member 122is then cured. The electrochromic cell is then placed fill port down inan empty container or trough in a vacuum vessel and evacuated.Electrochromic fluid media is introduced into the trough or containersuch that the fill port is submerged. The vacuum vessel is thenbackfilled which forces the fluid electrochromic material through thefill port and into the chamber 116. The fill port is then plugged withan adhesive, typically a UV light curing adhesive, and the plug materialis cured. This vacuum filling and plugging process is commonly used inthe LCD industry. If the proper polymeric bead material 117 is used, thebeads will dissolve in the electrochromic medium without leaving a traceat room temperature or by applying moderate heat as the electrochromicmedium gels thereby permanently fixing the cell gap.

[0046] Generally, these polymeric beads comprise a material that willreadily dissolve in organic solvents, such as, for example, propylenecarbonate, at ambient or near-ambient temperatures. The materials shoulddissolve in the electrochromic medium either within the time it takesthe free-standing gel to crosslink (which generally takes around 24hours), but not so fast that they do not provide a spacer functionduring processing (e.g., sealing and vacuum backfilling) of the mirrorelement. Materials that meet the above requirements include thefollowing copolymers available from ICI Acrylics, Wilmington, Del.:“ELVACITE” 2008, a MMA/methacrylic acid copolymer, “ELVACITE” 2010, aMMA/ethylacrylate copolymer, “ELVACITE” 2013, and a MMA/n-butylacrylatecopolymer, as well as poly(propylene carbonate), with “ELVACITE” 2013being presently preferred. In addition to these copolymers, it isbelieved that materials such as various polyacrylates and polyethers maybe suitable for the dissolvable beads.

[0047] Since the beads are used to maintain cell spacing for a shorttime during manufacture, they should preferably have a diameter equal toor slightly larger than the cell spacing of the device, which can beaccomplished by sieving through successive screens to obtain the desiredsize. Sieves of the appropriate size can be purchased from ATM,Milwaukee, Wis. If 135 micron glass beads will be loaded into thesealing resin, the preferred plastic bead size would be about 10% largeror 148 microns. To sieve plastic beads to the 148 micron range, astandard 145 micron and a standard 150 micron sieve would be required.If a tighter range is desired, custom-sized sieves could be ordered foran additional cost. The 150 micron sieve is placed on top of the 145micron sieve and the top 150 micron sieve is charged with unsizedplastic beads. The sieves are then vibrated such that beads smaller than150 microns will fall through the holes in the 150 micron sieve. Beadssmaller than 145 microns will fall through the bottom 145 micron sieve,and beads between 145 and 150 microns in size will be captured betweenthe 145 micron and the 150 micron sieves. If the beads tend to clump orstick together, effective separation can be achieved by flushing aliquid such as water through the sieve stack while vibrating the sieves.Beads wet-sieved in this manner must be thoroughly dried before use suchas by oven baking at 80° C. for 2 hours.

[0048] Electrochromic devices having a thin glass element/gelledelectrochromic medium/thin glass element configuration as providedherein can be used in a wide variety of applications wherein thetransmitted or reflected light can be modulated. Such devices includerearview mirrors for vehicles; windows for the exterior of a building,home or vehicle; skylights for buildings including tubular lightfilters; windows in office or room partitions; display devices; contrastenhancement filters for displays; light filters for photographic devicesand light sensors; and indicators for power cells as well as primary andsecondary electrochemical cells.

[0049] It will be understood that the term “glass” may be referred toherein as glass, coated glass, layered glass, and/or glass doped with,for example, metals, metal oxides, dyes, additives, and/or othercompounds or materials used to affect the transmission properties of aglass element.

[0050] The present invention is also directed to an electrochromicdevice which comprises: (1) a first glass element having an electricallyconductive material associated therewith, wherein the first elementcomprises a height (h₁) , a width (w₂) , a thickness (t₁), an innersurface, and an outer surface; (2) a second glass element having anelectrically conductive material associated therewith, wherein thesecond element comprises a height (h₂) , a width (w₂) , and a thickness(t₂), an inner surface, and an outer surface; (3) a cell spacing (c)which comprises a distance between the inner surface of the firstelement and the inner surface of the second element; (4) a gelledelectrochromic medium contained within a chamber positioned between thefirst and second elements; (5) wherein (h₁), (w₁), (t₁), (h₂), (w₂),(t₂), and (c) are numerical values in millimeters; and (6) wherein (h₁),(w₁), and (t₁) of the first element, and (h₂), (w₂), and (t₂) of thesecond element and (c) comprise numerical values such that the followinginequality is satisfied:${\frac{2{h_{1}^{5}\left( {1 - ^{{- 2}{({h_{1}/w_{1}})}^{2}}} \right)}}{t_{1}^{3}\left( {7.57 \times 10^{12}} \right)} + \frac{2{h_{2}^{5}\left( {1 - ^{{- 2}{({h_{2}/w_{2}})}^{2}}} \right)}}{t_{2}^{3}\left( {7.57 \times 10^{12}} \right)}} \geq {{.1}{(c).}}$

[0051] In accordance with the present invention, it has beenexperimentally determined that when (h₁), (w₁), and (t₁) of the firstelement and (h₂), (w₂), and (t₂) of the second element generate a valuefor the left side of the above-identified inequality that is greaterthan approximately 10% of the cell spacing (c), then a gelledelectrochromic medium is necessary to substantially preclude, amongother things, undesirable optical distortion associated with theelectrochromic device. Indeed, if the above-identified inequality issatisfied, then displacement or warping of at least one of the twoelements facilitates optical distortion. Such displacement or warpingcan become readily problematic for electrochromic devices which arelarger and/or thinner than, for example, conventional rearview mirrors,such as large scale electrochromic exterior mirrors for trucks and othermotor vehicles, as well as for electrochromic window applications—justto name a few.

[0052] The above-identified inequality was obtained by conducting finiteelemental analysis on glass elements to evaluate their degree ofdisplacement while under hydrostatic load. The displacement of eachelement was then correlated as a function its height, width, andthickness. With the upper threshold limit for allowable,non-objectionable element displacement being approximately 10% of thecell spacing for an associated electrochromic device, the followingelements were examined to determine whether or not a gelledelectrochromic medium was required in the associated electrochromicdevice: TABLE I Element Gelled Height: Cell ElectrochromicWidth:Thickness Spacing Inequality Medium Experiment (mm) (mm) SatisfiedRequired A  55:250:2.2 0.137 No No B 390:135:2.2 0.200 Yes Yes C150:245:1.6 0.180 No No-Approx- imate Threshold

[0053] As can be seen from Table I, an electrochromic device whichincorporates elements from experiment A does not require a gelledelectrochromic medium. However, if an electrochromic device incorporateselements from experiment B, then a gelled electrochromic medium isclearly required. Experiment C provides one example of an upperthreshold limit where a gelled electrochromic medium is not required.

[0054] The following additional illustrative examples are not intendedto limit the scope of this invention but to illustrate its applicationand use:

EXAMPLE 1

[0055] Several electrochromic devices containing a free-standing gelwere prepared as follows. A solution of 1.5114 grams ofbis(1,1′-3-phenylpropyl)-4,4′-dipyridinium bis(tetrafluoroborate) in37.02 grams of a copolymer of 1:10 isocyanate ethyl methacrylate/methylmethacrylate was mixed with a solution comprising 0.7396 grams ofBisphenol A, 0.4606 grams of 5,10-dimethyl-5,10-dihydrophenazine, 0.5218grams of Tinuvin P (Ciba Geigy, Tarrytown, N.Y.) in 57.36 grams ofpropylene carbonate. This mixture was vacuum backfilled into severalindividual devices having two 1.1 mm glass elements that were sealedtogether with an epoxy seal, with a 180 micron cell spacing, thatcontained polymeric spacer beads comprising poly(propylene carbonate),available from Sigma-Aldrich, “ELVACITE” 2008, 2010, 2013, and 2041,respectively. The gel formation was carried out at ambient temperatures(20-25 degrees Celsius). The devices were approximately 4″×6″ and weresubjected to a vibration test consisting of a five hundred G-appliedshock load with a 6 point random axis of rotation, with temperaturescycling repetitively from −100 degrees Celsius to 100 degrees Celsiusover a four minute ramp for a total of 25 cycles. These devices allshowed excellent vibrational resistance. Additionally, all of the spacerbeads dissolved within 24 hours from when the devices were filled withthe gel mixture.

EXAMPLE 2

[0056] Several electrochromic devices were prepared in accordance withExample 1, except the size of the device elements were approximately5″×9″. All of the spacer beads dissolved within 24 hours from when thedevices were filled with the gel mixture. These devices were subjectedto a pressure point resistance test. These parts, having significantarea, have inherent points at which they are more susceptible tobreakage under externally applied pressure. One of these points(approximately 0.5 inches form the edge) was selected for testing. Theseparts showed no breakage even at 1235 pounds, which represents themaximum attainable pressure on the testing equipment used (a ChattilonForce Measurement Gauge ET-110, with a rounded hard plastic finger of 1″diameter). Upon releasing the 1235 pounds of pressure, it was notedthat, due to the extreme pressure, the gel had been forced out from anarea approximately 0.5 inches in diameter immediately under the plastictest finger. The glass elements appeared to have contacted one anotheras well. Within moments after removing the external pressure, the gel“self-healed” and resumed its original position at the test point. Forcomparison, parts containing no free-standing gel and having glasselements with thicknesses of about 1.1 mm and PMMA beads showed glassbreakage at an average of 167 pounds.

[0057] While the invention has been described in detail herein inaccordance with certain preferred embodiments thereof, manymodifications and changes therein may be effected by those skilled inthe art without departing from the spirit of the invention. Accordingly,it is our intent to be limited only by the scope of the appending claimsand not by way of the details and instrumentalities describing theembodiments shown herein.

What is claimed is:
 1. An electrochromic device, comprising: a firstglass element having an electrically conductive material associatedtherewith, wherein said first element comprises a height (h₁) , a width(w₁) , a thickness (t₁), an inner surface, and an outer surface; asecond glass element having an electrically conductive materialassociated therewith, wherein said second element comprises a height(h₂) , a width (w₂), and a thickness (t₂), an inner surface, and anouter surface; a cell spacing (c) which comprises a distance betweensaid inner surface of said first element and said inner surface of saidsecond element; a gelled electrochromic medium contained within achamber positioned between said first and second elements; wherein (h₁),(w₁), (t₁), (h₂), (w₂), (t₂), and (c) are numerical values inmillimeters; and wherein (h₁), (w₁), and (t₁) of said first element, and(h₂), (w₂), and (t₂) of said second element and (c) comprise numericalvalues such that the following inequality is satisfied:${\frac{2{h_{1}^{5}\left( {1 - ^{{- 2}{({h_{1}/w_{1}})}^{2}}} \right)}}{t_{1}^{3}\left( {7.57 \times 10^{12}} \right)} + \frac{2{h_{2}^{5}\left( {1 - ^{{- 2}{({h_{2}/w_{2}})}^{2}}} \right)}}{t_{2}^{3}\left( {7.57 \times 10^{12}} \right)}} \geq {{.1}{(c).}}$


2. The electrochromic device according to claim 1 , wherein said firstand second elements are substantially linear.
 3. The electrochromicdevice according to claim 1 , wherein said first and second elements arebent to a convex shape.
 4. The electrochromic device according to claim1 , wherein said first and second elements are bent to an asphericshape.
 5. The electrochromic device according to claim 1 , wherein saidgelled electrochromic medium comprises a crosslinked polymer matrix. 6.An electrochromic device, comprising: a first glass element having anelectrically conductive material associated therewith, wherein saidfirst element comprises a height (h₁), a width (w₁), a thickness (t₁),an inner surface, and an outer surface; a second glass element having anelectrically conductive material associated therewith, wherein saidsecond element comprises a height (h₂) , a width (w₂) , and a thickness(t₂), an inner surface, and an outer surface; a cell spacing (c) whichcomprises a distance between said inner surface of said first elementand said inner surface of said second element; a gelled electrochromicmedium contained within a chamber positioned between said first andsecond elements; wherein (h₁), (w₁), (t₁), (h₂), (w₂), (t₂), and (c) areindependent numerical values in millimeters; and wherein (h₁), (w₁), and(t₁) of said first element, and (h₂), (w₂), and (t₂) of said secondelement and (c) comprise numerical values such that the followinginequality is satisfied:${\frac{2{h_{1}^{5}\left( {1 - ^{{- 2}{({h_{1}/w_{1}})}^{2}}} \right)}}{t_{1}^{3}\left( {7.57 \times 10^{12}} \right)} + \frac{2{h_{2}^{5}\left( {1 - ^{{- 2}{({h_{2}/w_{2}})}^{2}}} \right)}}{t_{2}^{3}\left( {7.57 \times 10^{12}} \right)}} \approx {or} \geq {{.1}{(c).}}$


7. The electrochromic device according to claim 6 , wherein said firstand second elements are substantially linear.
 8. The electrochromicdevice according to claim 6 , wherein said first and second elements arebent to a convex shape.
 9. The electrochromic device according to claim6 , wherein said first and second elements are bent to an asphericshape.
 10. The electrochromic device according to claim 6 , wherein saidgelled electrochromic medium comprises a crosslinked polymer matrix. 11.An electrochromic device, comprising: thin front and rear spaced glasselements, each having front and rear surfaces, wherein said frontelement comprises a height (h₁), a width (w₁), a thickness (t₁) and saidrear element comprises a height (h₂), a width (w₂), and a thickness(t₂); a layer of transparent conductive material disposed on said rearsurface of said front element and on said front surface of said rearelement; a reflector disposed on one side of said rear element providedthat, if said reflector is on said rear surface of said rear element,then said front surface of said rear element contains a layer of atransparent conductive material; a perimeter sealing member bondingtogether said front and rear spaced elements in a spaced-apartrelationship to define a chamber therebetween, where said chambercontains a free-standing gel comprising a solvent and a crosslinkedpolymer matrix, and wherein said chamber further contains at least oneelectrochromic material in solution with said solvent and, as part ofsaid solution, interspersed in said crosslinked polymer matrix; whereinsaid polymer matrix cooperatively interacts with said front and rearelements to form one thick, strong unitary member, and where saidreflector material is effective to reflect light through said chamberand said front element when said light reaches said reflector afterpassing through said front element and said chamber; a cell spacing (c)which comprises a distance between said rear surface of said frontelement and said front surface of said rear element; wherein (h₁), (w₁),(t₁), (h₂), (w₂), (t₂), and (c) are numerical values in millimeters; andwherein (h₁), (w₁), and (t₁) of said first element, and (h₂), (w₂), and(t₂) of said second element and (c) comprise numerical values such thatthe following inequality is satisfied:${\frac{2{h_{1}^{5}\left( {1 - ^{{- 2}{({h_{1}/w_{1}})}^{2}}} \right)}}{t_{1}^{3}\left( {7.57 \times 10^{12}} \right)} + \frac{2{h_{2}^{5}\left( {1 - ^{{- 2}{({h_{2}/w_{2}})}^{2}}} \right)}}{t_{2}^{3}\left( {7.57 \times 10^{12}} \right)}} \geq {{.1}{(c).}}$


12. The electrochromic device according to claim 11 , wherein said firstand second elements are substantially linear.
 13. The electrochromicdevice according to claim 11 , wherein said first and second elementsare bent to a convex shape.
 14. The electrochromic device according toclaim 11 , wherein said first and second elements are bent to anaspheric shape.
 15. The electrochromic device according to claim 11 ,wherein said polymer matrix results from crosslinking polymer chains andwhere said polymer chains are formed by polymerizing at least onemonomer selected from the group consisting of: methyl methacrylate;methyl acrylate; 2-isocyanatoethyl methacrylate; 2-isocyanatoethylacrylate; 2-hydroxyethyl methacrylate; 2-hydroxyethyl acrylate;3-hydroxypropyl methacrylate; vinyl ether n-butyl methyl methacrylate;tetraethylene glycol vinyl ether; glycidyl methacrylate; 4-vinylphenol;acetoacetoxyethyl methacrylate and acetoacetoxyethyl acrylate.
 16. Theelectrochromic device according to claim 15 , wherein said polymerchains are cross-linked by reaction with a compound having a functionalgroup selected from the group consisting of aromatic and aliphatichydroxyl; aromatic and aliphatic cyanato; aromatic and aliphaticisocyanato; aliphatic and aromatic isothiocyanato, with a functionalityof at least
 2. 17. The electrochromic device according to claim 15 ,wherein said polymer chains results from the polymerization of at leasttwo distinct monomers.
 18. The electrochromic device according to claim15 , wherein said at least two monomers are selected from the groupconsisting of: methyl methacrylate; methyl acrylate; 2-isocyanatoethylmethacrylate; 2-isocyanatoethyl acrylate; 2-hydroxyethyl methacrylate;2-hydroxyethyl acrylate; 3-hydroxypropyl methacrylate; vinyl ethern-butyl methyl methacrylate; tetraethylene glycol divinyl ether;glycidyl methacrylate; 4-vinylphenol; acetoacetoxyethyl methacrylate andacetoacetoxyethyl acrylate.
 19. The electrochromic device according toclaim 18 , wherein said at least two monomers are selected from thegroup consisting of: methyl methacrylate; 2-isocyanatoethylmethacrylate; 2-hydroxyethyl methacrylate; and glycidyl methacrylate.20. The electrochromic device according to claim 19 , wherein said atleast two monomers comprise 2-hydroxyethyl methacrylate and methylmethacrylate.
 21. The electrochromic device according to claim 20 ,wherein the ratio of 2-hydroxyethyl methacrylate to methyl methacrylateis about 1:10.
 22. The electrochromic device according to claim 20 ,wherein said polymer chains formed from at least 2-hydroxyethylmethacrylate and methyl methacrylate are crosslinked by a compoundhaving more than one functional group that will react with an activehydrogen.
 23. The electrochromic device according to claim 19 , whereinsaid at least two monomers comprise isocyanatoethyl methacrylate andmethyl methacrylate.
 24. The electrochromic device according to claim 23, wherein the ratio of isocyanatoethyl methacrylate to methylmethacrylate ranges from about 1:3 to about 1:50.
 25. The electrochromicdevice according to claim 24 , wherein the ratio of isocyanatoethylmethacrylate to methyl methacrylate is about 1:20.
 26. Theelectrochromic device according to claim 24 , wherein said polymerchains formed from at least isocyanatoethyl methacrylate and methylmethacrylate are crosslinked by a compound having a functional groupcontaining more than one active hydrogen.
 27. The electrochromic deviceaccording to claim 15 , wherein said polymer matrix is formed from atleast two distinct polymer chains, each of said at least two distinctpolymer chains comprise at least one monomer selected from the groupconsisting of methyl methacrylate and methyl acrylate polymerized withat least one monomer selected from the group consisting of 2-isocyanatoethyl methacrylate; 2-isocyanato ethyl acrylate; 2-hydroxyethylmethacrylate; 2-hydroxyethyl acrylate; 3-hydroxypropyl methacrylate;glycidyl methacrylate; 4-vinylphenol; acetoacetoxyethyl methacrylate;vinyl ether n-butyl methyl methacrylate and acetoacetoxyethyl acrylate,where said first and second polymer chains may be the same or different.28. The electrochromic device according to claim 27 , wherein said firstof said at least two polymer chains comprises a copolymer ofisocyanatoethyl methacrylate and methyl methacrylate and where saidsecond of said at least two polymer chains comprises a copolymer of2-hydroxyethyl methacrylate and methyl methacrylate.
 29. Theelectrochromic device according to claim 28 , wherein where the ratio ofisocyanatoethyl methacrylate and methyl methacrylate ranges from about1:3 to about 1:50 and where the ratio of 2-hydroxyethyl methacrylate andmethyl methacrylate ranges from about 1:3 to about 1:50.
 30. Theelectrochromic device according to claim 11 , wherein said cooperativeinteraction between said free standing gel and said front and rearelements makes said device resistant to bending and breaking.
 31. Theelectrochromic device according to claim 11 , further comprisingpolymeric beads disposed within said chamber.
 32. The electrochromicdevice according to claim 31 , wherein said beads comprise a materialthat will dissolve within an electrochromic device at ambient ornear-ambient temperatures within about 24 hours.
 33. The electrochromicdevice according to claim 32 , wherein said beads comprise a copolymerselected from the group consisting of: MMA/methacrylic acid,MMA/ethylacrylate, MMA/n-butylacrylate, and poly(propylene carbonate).34. The electrochromic device according to claim 32 , wherein said beadsdo not impart any refractive imperfections to said device.
 35. Theelectrochromic device according to claim 11 , wherein said layer oftransparent conductive material disposed on said rear surface of saidfront element is a multi-layer stack having a first layer with a highrefractive index, a second layer with a low refractive index and a thirdlayer with a high refractive index.